[PATCH] PCI/ERR: Resolve regression in pcie_do_recovery

[Jay Vosburgh <jay.vosburgh@canonical.com>]

	Commit 6d2c89441571 ("PCI/ERR: Update error status after
reset_link()"), introduced a regression, as pcie_do_recovery will
discard the status result from report_frozen_detected.  This can cause a
failure to recover if _NEED_RESET is returned by report_frozen_detected
and report_slot_reset is not invoked.

	Such an event can be induced for testing purposes by reducing
the Max_Payload_Size of a PCIe bridge to less than that of a device
downstream from the bridge, and then initating I/O through the device,
resulting in oversize transactions.  In the presence of DPC, this
results in a containment event and attempted reset and recovery via
pcie_do_recovery.  After 6d2c89441571 report_slot_reset is not invoked,
and the device does not recover.

	Inspection shows a similar path is plausible for a return of
_CAN_RECOVER and the invocation of report_mmio_enabled.

	Resolve this by preserving the result of report_frozen_detected if
reset_link does not return _DISCONNECT.

Fixes: 6d2c89441571 ("PCI/ERR: Update error status after reset_link()")
Signed-off-by: Jay Vosburgh <jay.vosburgh@canonical.com>

---
 drivers/pci/pcie/err.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
index 14bb8f54723e..e4274562f3a0 100644
--- a/drivers/pci/pcie/err.c
+++ b/drivers/pci/pcie/err.c
@@ -164,10 +164,17 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
 
 	pci_dbg(dev, "broadcast error_detected message\n");
 	if (state == pci_channel_io_frozen) {
+		pci_ers_result_t status2;
+
 		pci_walk_bus(bus, report_frozen_detected, &status);
-		status = reset_link(dev);
-		if (status != PCI_ERS_RESULT_RECOVERED) {
+		/* preserve status from report_frozen_detected to
+		 * insure report_mmio_enabled or report_slot_reset are
+		 * invoked even if reset_link returns _RECOVERED.
+		 */
+		status2 = reset_link(dev);
+		if (status2 != PCI_ERS_RESULT_RECOVERED) {
 			pci_warn(dev, "link reset failed\n");
+			status = status2;
 			goto failed;
 		}
 	} else {
-- 
2.7.4